The present invention relates generally to data transmission in communication systems and more specifically to methods and systems for facilitating multi-carrier and coordinated multi-point operation in a mobile communication system.
As used herein, the terms “user agent” and “UA” can refer to wireless devices such as mobile telephones, personal digital assistants, handheld or laptop computers, and similar devices or other User Equipment (“UE”) that have telecommunications capabilities. In some embodiments, a UA may refer to a mobile, wireless device. The term “UA” may also refer to devices that have similar capabilities but that are not generally transportable, such as desktop computers, set-top boxes, or network nodes.
In traditional wireless telecommunications systems, transmission equipment in a base station or other network node transmits signals throughout a geographical region known as a cell. As technology has evolved, more advanced equipment has been introduced that can provide services that were not possible previously. This advanced equipment might include, for example, an evolved universal terrestrial radio access network (E-UTRAN) node B (eNB) rather than a base station or other systems and devices that are more highly evolved than the equivalent equipment in a traditional wireless telecommunications system. Such advanced or next generation equipment may be referred to herein as long-term evolution (LTE) equipment, and a packet-based network that uses such equipment can be referred to as an evolved packet system (EPS). Additional improvements to LTE systems and equipment will eventually result in an LTE advanced (LTE-A) system. As used herein, the phrase “base station” will refer to any component, such as a traditional base station or an LTE or LTE-A base station (including eNBs), that can provide a UA with access to other components in a telecommunications system.
In mobile communication systems such as the E-UTRAN, a base station provides radio access to one or more UAs. The base station comprises a packet scheduler for dynamically scheduling downlink traffic data packet transmissions and allocating uplink traffic data packet transmission resources among all the UAs communicating with the base station. The functions of the scheduler include, among others, dividing the available air interface capacity between UAs, deciding the transport channel to be used for each UA's packet data transmissions, and monitoring packet allocation and system load. The scheduler dynamically allocates resources for Physical Downlink Shared CHannel (PDSCH) and Physical Uplink Shared CHannel (PUSCH) data transmissions, and sends scheduling information to the UAs through a control channel.
To facilitate communications, a plurality of different communication channels are established between a base station and UA 10 including, among other channels, a Physical Downlink Control Channel (PDCCH). As the label implies, the PDCCH is a channel that allows the base station to control UA 10 during downlink data communications. To this end, the PDCCH is used to transmit scheduling assignment or control data packets referred to as Downlink Control Information (DCI) packets to the UA 10 to indicate scheduling to be used by UA 10 to receive downlink communication traffic packets on a Physical Downlink Shared Channel (PDSCH) or transmit uplink communication traffic packets on Physical Uplink Shared Channel (PUSCH) or specific instructions to the UA (e.g. power control commands, an order to perform a random access procedure, or a semi-persistent scheduling activation or deactivation). A separate DCI packet may be transmitted by the base station to UA 10 for each traffic packet/sub-frame transmission.
It is generally desirable to provide high data rate coverage using signals that have a high Signal to Interference Plus Noise ratio (SINR) for UAs serviced by a base station. Typically, only those UAs that are physically close to a base station can operate with a very high data rate. Also, to provide high data rate coverage over a large geographical area at a satisfactory SINR, a large number of base stations are generally required. As the cost of implementing such a system can be prohibitive, research is being conducted on alternative techniques to provide wide area, high data rate service.
In some cases, carrier aggregation can be used to support wider transmission bandwidths and increase the potential peak data rate for communications between UA, base station and/or other network components. In carrier aggregation, multiple component carriers are aggregated and may be allocated in a sub-frame to a UA as shown in FIG. 1. FIG. 1 shows carrier aggregation in a communications network where each component carrier has a bandwidth of 20 MHz and the total system bandwidth is 100 MHz. As illustrated, the available bandwidth 100 is split into a plurality of carriers 102. UA may receive or transmit on multiple component carriers (up to a total of five carriers 102 in the example shown in FIG. 1), depending on the UA's capabilities. In some cases, depending on the network deployment, carrier aggregation may occur with carriers 102 located in the same band and/or carriers 102 located in different bands. For example, one carrier 102 may be located at 2 GHz and a second aggregated carrier 102 may be located at 800 MHz.
Additionally, coordinated multi-point (CoMP) transmission and reception may be used to increase transmission data rate and/or signal quality in wireless communication networks such as LTE-A networks. Using CoMP, neighboring base stations may coordinate to improve the user throughput or signal quality, especially for users at the cell edge. CoMP may be implemented using a combination of base stations such as eNBs, remote radio heads and/or relay nodes (RN) and/or other types of network nodes and/or cells.
In communication networks implementing CoMP, difficulties may arise when different numbers of multiple carriers are deployed among combinations of base stations or other network nodes such as eNBs, RNs, and/or cells. For example, an eNB, RN or cell in a first hotspot location may have 5 carriers deployed while another eNB, RN or cell that is not in a hotspot location may only have 2 carriers deployed. In that case, to implement successful cooperation and coordination of eNBs, RNs, and/or cells for CoMP it may be necessary to consider the set of carriers deployed in and made available by each cooperating eNB, RN, network node or cell individually.